Defrosting machine



1954 E. TOOTHMAN 2,693,683

DEFROSTING MACHINE Filed May 3 1951 2 Sheets-Sheet l CONDENSER EECE/VEEINVENTOR. E/IEL T00 THMAN 2 Sheets-Sheet 2 1954 E. TOOTHMAN DEFROSTINGMACHINE Filed May 3, 1951 N MIHMIH IN V EN TOR.

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EAEL Toormm/v United States Patent C DEFROSTING MACHINE Earl Toothman,San Francisco, Calif., assignor of onehalf to Edward A. Danforth, PaloAlto, Calif.

Application May 3, 1951, Serial No. 224,319

7 Claims. (Cl. 62-11755) This invention relates to a defrosting systemand, more particularly, to a defrosting system for refrigeration unitswhich employs hot gases from the compressor to heat, and therebydefrosts the evaporator coils.

In refrigeration systems employing a compressor, a condenser andevaporating coils and wherein a gas such as ammonia is compressed by thecompressor and is then condensed in the condenser and evaporated inevaporating coils to cause refrigeration, the coils ice up or frostowing to condensation and freezing of water in the atmosphere.

Several defrosting systems have been suggested, and some of them arecurrently employed for automatically defrosting the evaporator coils.One type of automatic defrosting system employs the hot, compressedgases from the compressor as a source of heat to heat the coils. Forthis purpose by-pass means are provided for by-passing the condenser andconducting the hot gases directly to the evaporator coils. The by-passmeans includes suitable valves, solenoids for operating the same andelectrical timing means for operating the solenoids at predeterminedintervals.

Certain dilficulties or disadvantages have been encountered in theinstallation and/or operation of prior automatic, hot gas defrostingsystems. In one such system, during the refrigeration cycle hot gas fromthe compressor is passed through a heat storage vessel or reservoircontaining a body of liquid. The hot gas heats the liquid, and this heatis employed during the defrosting cycle to vaporize liquid from theevaporator coils. In this system, the liquid, which constitutes the heatstorage medium, is cooled very rapidly during the defrosting cycle, somuch so that the liquid from the evaporator coils is not fullyvaporized.

In another system, a direct heat exchange is provided during thedefrosting cycle, between the hot gas from the compressor and the coldliquid from the evaporator coils. However, in this system, no provisionis made for storage of liquid from the evaporator coils during thedefrosting cycle. The refrigerant passes directly from the evaporatorcoils to the compressor. As a result, the supply of vapor in the suctionline of the compressor is likely to be exhausted and, when this occurs,the compressor will simply pump liquid to the evaporator coils.

It is an object of the present invention to provide improved automaticdefrosting means for refrigeration systems.

It is a further object of the invention to provide improved automaticdefrosting means of the hot gas type for refrigeration systems.

Yet another object of the invention is to provide a hot gas defrostingsystem which obviates certain disadvantages of systems employedheretofore.

A further object of the invention is to provide a hot gas defrostingsystem which avoids the need for maintaining a supply of liquid to actas a heat reservoir.

Yet another object of the invention is to provide a hot gas defrostingsystem in which there is little or no likelihood of circulating liquidfrom the evaporator coils to the compressor, thence back to theevaporator coils.

Another object of the invention is to provide a hot gas defrostingsystem which can be easily and readily installed in an existingrefrigeration system with a minimum of effort in the way of newconnections and changes in the existing system.

These and other objects of the invention will be ap- 0 parent from theensuing description and appended claims;

7 2,693,683 Patented Nov. 9, 1954 Certain forms of the invention areillustrated by way of example in the accompanying drawing and aredescribed in detail hereinafter.

In the drawings:

Figure 1 is a diagrammatic view of a refrigeration system includingautomatic defrosting means constructed in accordance with the invention;

Figure 2 is a diagrammatic view of a defrosting system constructed inaccordance with the invention, as applied to an existing refrigerationsystem.

Referring to Figure 1, a refrigeration system is there shown whichincludes the usual compressor 10, condenser 11, receiver 12 andevaporator coils 13. During normal operation of the system a suitablegas, such as ammonia, is compressed in the compressor 10. It is thenconducted through a conduit 14 to the condenser 11 and is therecondensed to a liquid, and the liquid refrigerant is then conductedthrough a conduit 15 to the receiver 12 for storage. From the receiverthe liquid refrigerant is conducted through a conduit 16 and is expandedby an expansion valve 17 into a header 18, thence into the evaporatorcoils 13. Suitable automatic means well-known in the art, such as afeeler bulb (not shown), may be employed to operate the expansion valveso as to maintain suitable refrigeration conditions. Drip pan coils 20are also provided, as is a fan driven by a motor/31 for circulating airover the coils.

The expanded gas from the coils, which may be partly liquefied, isreturned to the compressor through a conduit 32. However, it is notreturned directly to the compres sor. Instead, and in accordance with myinvention, it is conducted first to an accumulator vessel 33 from whichthe vapor passes through a conduit 34 to an outer vessel 35 which formsa part of a heat exchanger and re-evaporator 36. Thence the vapor passesthrough a suction line 37 to the inlet of the compressor.

It will be seen that my system also includes a conduit 38 which isconnected to the outlet of the compressor to by-pass the condenser andwhich communicates with, and extends to the bottom of an inner vessel 39which is disposed within the outer vessel 35, and which also forms apart of the heat exchanger 36. Thence a hot gas line 40 leads to thedrip pan coils 20 which are connected to the evaporator coils 13 througha conduit 41 containing a check valve 42, and through the conduit 16. Anormally closed valve 45 is provided in the conduit 38 which is openedby a solenoid 46 when the latter is energized.

Another feature of the present invention comprises a connection betweenthe vapor space in the receiver 12 and the outer vessel 35 through themedium of a conduit 47 containing a normally closed valve 48 which isopened when a solenoid 49 is energized. A manually operable shut-offvalve 50 is also provided.

Electric current is provided for operating the defrosting system by acircuit comprising a timing switch 51 which may be of standardconstruction, a power lead 52 connected to each of the solenoids 46 and49 and through a branch lead 52a to the fan motor 31, a power lead 53connected to a terminal of the time switch and leads 54 and 55connecting other terminals of the time switch with the fan motor 31 andthe solenoids 46 and 49, respectively.

Operation during the refrigeration cycle proceeds as described above; i.e., gas is compressed in the compressor 16 and passes through theconduit 14 to the condenser 11 where it is condensed. It then passesthrough the conduit 15 to the receiver 12. The liquid refrigerant thenpasses through the conduit 16 and expansion valve 17 and is expandedinto the evaporator coils 13 from which it returns to the condenser byway of the suction line 32 to the accumulator vessel 33, thence throughcon- .duit 34 to the outer vessel 35, thence through suction line 37 tothe inlet of the compressor. At predetermined intervals, in accordancewith the setting of time switch 51, the valves 45 and 48 are opened bythe solenoids 46 and 49. At the same time the motor 31 and fan 30 arestopped. When the valves 45 and 48 are opened, hot gases from thecompressor by-pass the condenser 11 and pass through the conduit 38 tothe inner vessel 39 of the heat exchanger 36, thence through the hot gasline 40 to the drip pan coils 20 and, through the check valve 42 andlines 41 and 16, to the evaporator coils 13. Defrosting is therebyaccomplished by passage of the hot gases through the coils 20 and 13. Inpassing through the coils 20 and 13, the hot compressorgases will pushthrough the coils liquid refrigerant which remains in the coils at theend of the refrigeration cycle. Also, to some extent the hot gasesthemselves may be condensed. This liquid refrigerant passes, along withthe gases, through the conduit 32 to the accumulator vessel 33, whichserves as a the evaporator coils 13 and the heat exchanger 36, onlyvapor can reach the heat exchanger.

Hence, liquefied refrigerant cannot reach' the compressor; only vaporcan reach it. This vapor is effectively heated in. the heat exchanger 36by heat interchange with the hot compressor gases. An ample supply ofvapor for the compressor is assured by reason of the body of liquidrefrigerant in the accumulator vessel '33 and' in the receiver 12'. Bothof these vessels are in communication with the vessel 35 during thedefrosting cycle, and provide an. ample supply of vapor. The heatinterchange between incoming vapor and outgoing hot gases in the'heat'exchanger prevents supplying any liquid refrigerantto the compressor.

At the conclusion of the defrosting cycle, the solenoids 46 and 49 willbe tie-energized and the valves 45 and 438 will assume their normallyclosed positions to restore the system to normal refrigeratingconditions.

Referring now to Figure 2, in which parts similar to those in Figure lare similarly numbered;.a modified form of defrosting system isillustrated which is adapted for use with an existing refrigerationsystem. The. refrigeration system comprises a compressor 10,. acondenser 11, av receiver 12 and evaporator coils 13. Spent refrigerantis returned to the compressor through a conduit 32a containing anormally open valve 60 which is closed only when a solenoid 61 isenergized through leads .62. A separate defrosting system is providedwhich is generally designated as 65. This defrosting system comprises anaccumulator vessel 33 and a heat exchanger 36, as in the case of thedefrosting system of Figure l and, as in the case of Figure l, the heatexchanger includes an outer vessel 35 and an inner vessel 39. Thissystem is connected with the refrigeration system in the-followingmanner: The outlet conduit 14 f the compressor 10 is connected through aconduit 66 and a normally closed valve 67 to the bottom of the innervessel39. The valve 67 is opened by a. solenoid 68 when the latter isenergized through leads 69'. A hot gas line 46 connects the upper end ofthe inner vessel 39 tothe drip pan coils 2.0 and the evaporator coils13, and the outlet end ofthe evaporator coils 13 is connected through aconduit 32 to the accumulator vessel 33. The upper end of. theaccumulator vessel 33 is connected through a. conduit 34 containing ahand valve 70 to the outer vessel 35 and the bottom of the accumulatorvessel 33 is connected through a conduit 71 and an expansion valve 72 toa nozzle '73 which is so located as to spray fluid onto the outersurface of the inner vessel 39. A conduit 74 connects the outer vessel35 with the inlet of the compressor 10.

In operation the refrigeration system will operate in essentially themanner as described above with reference to Figure l; i. e., hotcompressed gases from the compressor will pass through the conduit 14into the condenser 11 and the condensed refrigerant will pass throughthe conduit 15 to the receiver 12, thence through the conduit 16 andexpansion valve 17 into the evaporator coils '13. However, instead ofreturning to the compressor through the defrosting system asin thesystem of Figure 1, the spent refrigerant will return directly to thecompressor through the conduit 32a.

At predetermined intervals, in accordance with the setting of a timeswitch (not shown), the solenoids 61 and 68 will be energized to closethe valve 60 and open the valve 67. Hot gases from the compressor willthen pass through the conduit 66 to the inner vessel 39 of the heatexchanger 36 and will then pass through theconduit 40 to thedrippancoils'2tl' and the evaporator coils 13.

4 Liquid refrigerant and spent gas or vapor from the evaporator coils 13will pass through the conduit 32' to the accumulator vessel 33. Vaporfrom the upper end of the accumulator vessel 33 will pass through theconduit 34 to the outer vessel 35 of the heat exchanger 36 and will beheated therein by the hot gases in the inner vessel 39. The warm vaporwill then pass through the conduit 7 4 to the inlet of the compressor10.

Liquid refrigerant. in the accumulator Vessel 33 will pass through theconduit 71, will be expanded by the expansion valve 72 and will besprayed by the nozzle 73 against the warm outer surface of the innervessel 39. Liquid thus transferred from the accumulator vessel 33 to theheat exchanger will be instantly vaporized by the hot gases in the innervessel 39 and the vapor will be drawn through the conduit 74 into theinlet of the compressor 10. There is an important advantage in this modeof operation, which can be explained as follows: As is well known, inthe operation of a refrigeration system the lubricant employed tolubricate the cornpressor'will find its way into the evaporator coils.When hot gas is introduced into the coils during, defrosting, it willpush the lubricant from these coils along with liquid refrigerant. Anefiicient re-evaporator will evaporate the liquid refrigerant but itwill not evaporate the lubricant, because its vapor pressure is muchlower than that of the refrigerant. It is highly undesirable to returnliquid lubricant to the suction line of the compressor; slugging andother undesirable results will occur. Heretofore it has been a commonpractice to collect lubricant in a trap and return it to the crankcaseof the compressor. 7 i

The: expansion: valve 72 and the nozzle 73 shown in Figure 2 provide ameans for returning lubricant to the compressor without slugging andwithout using a lubricant trap.

As explanied above, when the liquid refrigerant is sprayedonto the warmouter surface of the inner vessel 39, it is instantly vaporized: Byreason of this instant vaporization or flashing of liquid refrigerant,and by reason of spraying the liquid refrigerant and entrainedcompressor lubricant, the lubricant is necessarily atomized and finelydispersed in the refrigerant vapor. The resulting fine dispersion ofliquid lubricant in refrigerant vapor is then supplied to the suctionline of the cornpressor without the above-mentioned difficulties andwithout'th ecessity of using a lubricant'trap.

After installation ofthe defrosting system of Figure" 2, the hand valve70' will be adjusted manually until the defrosting system isoperatingproperly. Thereafter, further adjustment of valve 70 isunnecessary eXcept' occasionally.

It willthus be apparent that a defrosting system has been provided whichis effective to defrost evaporator coils. of an automatic refrigerationunit by the action of the hot gases from the compresson. In one of itsforms, this defrosting. systeniis adapted to. installation as anintegral part of a refrigeration system; In another form it is adaptedto installation as a separate unit in an existing refrigeration unit.The defrosting system of the present invention obviates certaindisadvantages which have been encountered in previous hot gas defrostingsystems. Thus, the necessity of maintaining and heating a body of liquidis obviated. Also an ample supply of vapor for the compressor is assuredat'all times. The defrosting s. stem vof the ,presentinvention is simpleto install and to operate and it is dependable in its operation. V

Iclaim;

1. In apparatus ofthe character descri'bed comprising a closedrefrigeration system including a compressor, a condenser, and anevaporator. and a closed hot. gas defrosting system forperiodicallivlby-passing. thec ndenSer and circulating hot gas fromcompressor to the evaporator, thence back to. the compressor, theimprovement which comprises: an accumulator vessel. for receivingrefrigerant. from the evaporator during the defrosting cycle and forstoring liquid refrigerant so. received; and heat exchange meansinterposed. between the accumulator vessel and the compressor forreceiving refrigerant from the accumulator vessel and heatingit by heattransferred from hot gas from the compressor during the defrosting cyclan mean in rconn ctings i accumulator v l and'hcat exchange .mans;lsa;id accumulatorv sel hav s a capacitysufficient to receive andentrap the entire'volume of liquid contained in the evaporator at thecommencement of the defrosting cycle; said interconnecting means beingsuch as to prevent the passage of continuous liquid phase from theaccumulator vessel into the heat exchange means but to permit passage ofvapor or or finely dispersed liquid from the accumulator vessel into theheat exchange means.

2. In apparatus of the character described comprising a closedrefrigeration system including a compressor, a condenser and anevaporator and a closed hot gas defrosting system for periodicallyby-passing the condenser and circulating hot gas from the compressor tothe evaporator, thence back to the compressor, the improvement whichcomprises: an accumulator vessel for receiving refrigerant from theevaporator during the defrosting cycle and for storing the entire volumeof liquid contained in the evaporator at the commencement of thedefrosting cycle; heat exchange means interposed between the accumulatorvessel and the compressor for receiving refrigerant from the accumulatorand heating it by heat transferred from hot gas from the compressorduring the defrosting cycle; and means for transferring vapor from theaccumulator vessel to the heat exchanger, such means preventing passageof continuous liquid phase from the accumulator vessel into the heatexchanger.

3. A refrigeration system comprising a compressor, a condenser, areceiver and an evaporator and means connecting the said elements toprovide a closed refrigeration system; and a closed, hot gas defrostingsystem for periodically by-passing the condenser and circulating hot gasfrom the compressor to the evaporator, thence back to the compressor;said hot gas defrosting system comprising an accumulator vessel forreceiving refrigerant from the evaporator during the defrosting cycleand for storing liquid refrigerant so received; a heat exchangerinterposed between the accumulator vessel and the compressor forreceiving refrigerant from the accumulator and heating it by heatexchange with hot gas from the compressor; and means connecting thereceiver with the heat exchanger to supply vaporized refrigerant theretoduring the defrosting cycle, said means comprising a conduit providingsuch connection and an automatic valve in said conduit which is closedduring the refrigeration cycle and open during the defrosting cycle.

4. A refrigeration system comprising a compressor, a condenser, areceiver and an evaporator and means connecting said elements to providea closed refrigeration system; and a hot gas defrosting system therefor,said defrosting system comprising an accumulator vessel, a heatexchanger comprising a first vessel for receiving hot gases and a secondvessel for receiving cold refrigerant, means connecting the outlet ofthe evaporator with said accumulator, means connecting accumulator withsaid second vessel to supply cold refrigerant vapor thereto, meansconnecting said second vessel with the inlet of said compressor, meansconnecting the outlet of the said compressor with said first vessel,means connecting said first vessel with the inlet of said evaporator,and means connecting said receiver with said second vessel for supplyingvaporized refrigerant thereto.

5. A hot gas defrosting system comprising a compressor having an outletfor hot compressed gas and an inlet, an evaporator for evaporatingcondensed refrigerant, a heat exchanger, an accumulator vessel having acapacity suflicient to receive and entrap the entire volume of liquidcontained in the evaporator at the commencement of the defrosting cycle;said system also comprising a defrosting circuit for conducting hot gasduring the defrosting cycle from the compressor outlet through the heatexchanger to the evaporator, for passing spent vapor and liquid expelledfrom the evaporator to said accumulator, for passing refrigerant vaporfrom the accumulator to the heat exchanger Without passing continuousliquid phase thereto, and for passing refrigerant vapor from the heatexchanger to the compressor inlet.

6. A hot gas defrosting system comprising an accumulator vessel forreceiving spent vapor and liquid refrigerant from the evaporator of arefrigeration system, a heat exchanger comprising inner vessel and anouter vessel in heat exchange relation, means for supplying hotcompressed gas to said evaporator through said inner vessel, means forreturning spent vapor and liquid refrigerant from the evaporator to saidaccumulator vessel, means for conducting liquid refrigerant from saidaccumulator vessel to said outer vessel and for spraying same on thesurface of said inner vessel, and means for conducting heatedrefrigerant vapor from said outer vessel to said compressor.

7. A refrigeration system comprising a compressor, a condenser, areceiver and an evaporator and means connecting' said elements toprovide a closed refrigeration system; and a hot gas defrosting systemtherefor, said defrosting system comprising an accumulator vessel havinga capacity sufiicient to receive and entrap the entire volume of liquidcontained in the evaporator at the commencement of the defrosting cycle,a heat exchanger comprising a first vessel for receiving hot gases and asecond vessel for receiving cold refrigerant, means connecting theoutlet of the evaporator with said accumulator, means connecting theaccumulator with said second vessel to supply cold refrigerant vaporthereto Without supplying continuous liquid phase thereto, meansconnecting said second vessel with the inlet of said compressor, meansconnecting the outlet of the said compressor with said first vessel, andmeans connecting said first vessel with the inlet of said evaporator.

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